Preparation of olefinically-unsaturated organic acids



IPLR'EIPARATION F OLEFINICALLY-UNSATU- RATED ORGANIC ACIDS W. Va.,assignors to Union Carbide Corporation, a corporation of New York NoDrawing. Application March 21, 1957 Serial No. 647,481

12 Claims. (Cl. 260 526) This invention is directed to a process for theproduction of olefinically-unsaturated organic acids. More particularly,this invention is directed to the pyrolysis of epsilon-caprolactones toproduce the olefinically-unsaturated acids and has for an object theprovision of a process for manufacturing olefinically-unsaturated acidsof a predetermined type. More specifically, it is an object of thisinvention to provide a process for the production ofdelta-olefinically-unsaturated organic acids from the correspondingepsilon-caprolactones, and in the case ofepsilon-alkyl-epsilon-caprolactones, epsilon-olefinicallyunsaturatedorganic acids. A particular object of the invention is to provide aprocess for the; production of delta-hexenoic acid to the substantialexclusion of gammahexenoic acid which comprises pyrolyzingepsiloncaprolactone.

Heretofore, according to customary practices, the

methods of producing olefinically-unsaturated acids from lactonesinvolve the hydrolysis of the lactone to the corresponding hydroxy acidsfollowed by dehydration to provide the corresponding unsaturated acidsusually as a mixture of isomers. Random distribution of isomers occursand it is impossible, from a practical standpoint, to isolate therespective isomers.

. By virture of the process of this invention, random distribution ofisomers is substantially avoided and olefinically-unsaturated acids of adesired type can now be produced with greater selectivity and ease.

Quite unexpectedly it has been discovered that epsiloncaprolactones canbe cracked under pyrolysis conditions whereas the corresponding deltaandgamma-lactones cannot. This is indeed surprising in view of the factvthat S-mernbered rings have substantially the same degree of strain asthe 7-membered rings, yet when the gammalactones are subjected topyrolysis conditions they do not crack. Normally, it would be expectedthat the epsilonc aprolactones would be similar in reactivity to thegammaand delta-lactones. p

f It has been discovered that epsilon-caprolactones can bepyrolyzedtospecific unsaturated acids to the substant-ial exclusion of undesirablemixtures of isomer which are normally to be expected under conditionsinvolving hydrolysis and dehydration of the epsiloncaprolactone asdiscussed, supra. As used herein the term substantial exclusion? isintended to mean the production of a reaction mixture containing thedesired isomer in predominating amounts and the undesired isomer inamounts of the order of less than ten percent by weight of the totalcontained unsaturated acids.

: The process of this invention is directed to the preparation of'olefinically-unsaturated acids from epsiloncaprolactones correspondingto the general formula:

United States Patent Patented Mar. 3, 1959 ice wherein, R, R R and Yrepresent hydrogen atoms and lower alkyl groups containing from 1through 8 carbon Epsilon-caprolactoneGamma-isopropyl-epsilon-caprolactone Alpha-methyl-epsilon-caprolactoneBeta-methyl-epsilon-caprolactone Gamma-methyl-epsilon-caprolactoneDelta-methyl-epsilon-caprolactone Epsilon-methyl-epsilon-caprolactoneAlpha-ethyl-cpsilon-caprolactone Beta-ethyl-epsilon-caprolactoneGamrna-ethyl-epsilon-caprolactone Delta-ethyl-epsilon-caprolactoneEpsilon-ethyl-epsilon-caprolactoneAlpha,beta-dirnethyl-epsilon-caprolactoneAlpha,gamma-dimethyl-epsilon-caprolactone Alpha,delta-dimethyl-epsiloncaprolactone Alpha,epsilon-dimethyl-epsilon-caprolactoneBeta,gamma-dimethyl-epsilon-caprolactoneBetta,delta-dirnethyl-epsilon-caprolactoneBeta,epsilon-dimethyl-epsilon-caprolactoneGamma,delta.dimethyl-epsilon-caprolactone Gammaepsilon-dimethyl-epsilon-caprolactoneDelta-epsilon-dimethyl-epsilon-carprolactoneBeta,beta,delta-trimethyl-epsilon-caprolactoneAlpha,beta,gamma-trimethyl-epsilon-caprolactoneAlpha,beta,delta-trimethyl-epsilon-caprolactoneAlpha,beta,epsilon-trimethyl-epsilon-caprolactoneBeta,gamma,delta-trimethyl-epsilon-caprolactoneBeta,gamma,epsilon-trirnethyl-epsilon-caprolactoneGamma,delta,epsilon-trimethyl-epsilon-caprolactoneAlpha,ethyl-beta-methyl-epsilon-caprolactoneA!pha-cthyl-gamma-methyl-epsilon-caprolactoneAlpha-ethyl-delta-methyl-epsilon-caprolactoneAlpha-ethyl-epsilon-methyl-epsilon-caprolactoneBeta-ethyl-alpha-methyl-epsilon-caprolactoneBeta-ethyl-gamma-methyl-epsilon-caprolactoneBeta-ethyl-delta-methyl-epsilon-caprolactoneBeta-ethyl-epsilon-metbyl-epsilon-caprolactoneGamma-ethyl-alpha-methyl-epsilon-caprolactoneGamma-ethyl-beta-methyl-epsilon-caprolactoneGamma-ethyl-delta-methyl-epsilon-caprolactoneGamma-ethyl-epsiion-methyl-epsilon-caprolactoneDelta-ethyl-alpha-methyl-epsilon-caprolactoneDelta-ethyl-beta-methyl-epsilon-caprolactoneDelta-ethyl-gamma-methyl-epsilon-caprolact0neDelta-ethyl-epsilon-methyl-epsilon-caprolactoneEpsilon-ethyl-alpha-methyl-epsilon-caprolactoneEpsiIon-ethyl-beta-methyl-epsilon-caprolactoneEpsilon-ethyl-gamma-methyl-epsilon-caprolactoneEpsilon-ethyl-delta-methyl-epsilon-caprolactoneAlpha,alpha-dimethyl-epsilon-caprolactoneBeta-beta-dirnethyl-epsilon-caprolactoneGamma,gamma-dimethyl-epsilon-caprolactone'Alpha,alpha,delta-trimethyl-epsilon-caprolactoneBeta,beta,gamma-trimethyl-epsilon-caprolactone Gam ma,gamma,epsilon-trimethyl-epsilon-caprolactoneBeta,beta-dimethyl-gamma-ethyl-epsilon-caprolactone As used herein theterm pyrolyzing is intended to mean cracking or theepsilon-caprolactones or heating to a temperature sufiici'ently high tocrack the epsilon-captolactones and includes conditions of temperatureof from, at, or above the boiling point of the selected caprolactonestarting material to. about 800 C. More particularly, the pyrolysisconditions of this invention involve temperatures of the order of fromabout 400 C. to about 600 -C.' at normal atmospheric pressures.

It has" been determined that the residence time for optimum conversionin the reaction zone of the heated selected epsilon-caprolactone is afunction of the temperature of the reaction. It has been found that atthe temperatures above specified, the reaction can be accomplished at arate of from about 20 ml. per hour to about 1000 ml. per. hour in aheated zone one inch in diameter and, three feet long. atpractica'lefiiciencies of epsiloncaprolactonesto unsaturated acids. Expressed interms of space velocity (liters/liter/hour) practical yields andconversions of epsilon-caprolactones are obtained at' space velocitiesof from 20. to 3000 approximately.

In carrying out the process of this invention an. epsiloncaprolactone,such as epsilon-caprolactone, is fed at a rate of from about 200 ml. perhour through a pyrolysis tube such as a stainless steel tube (1 inch by36 inches.) preferably packed with Fiitros or glass beads to give anapproximate free space of 70 percent at a temperature of 560 C. Theefiiuent from the pyrolysis tube is analyzed for acid content.

The pyrolysis mixture maybe analyzed for acid by titration with base.Water and ice are usually added to the sample for analysis and the coldmixture is titrated quickly with 0.5 N sodium hydroxide or potassiumhydroxide. Under these conditions the lactone ring is. not opened by thebase.

Isolation of the unsaturated acids is simplified when a high conversionper pass is obtained since the starting lactone and the unsaturated acidusually boil fairly near each other. However, pyrolysis efficiencies areusually better, especially in the case of epsilon-caprolactone, if theconditions chosen are mild enough to avoid large amounts of gasformation during, the pyrolysis. The products may be isolated by theusual methods such as fractional distillation or extraction of the acidby means of sodium. bicarbonate or sodium carbonate at low temperaturesfrom a solution of the reaction mixture in chloroform or some otherwater-insoluble solvent. The unused epsilon-caprolactone may then berecycled back to the pyrolysis tube.

Example I Epsilon-caprolactone (100 ml.) was fed at the rate of 200ml./hr. through a stainless steel tube (1 inch by 36 inches) packed withFiltros which was heated to 440- 450 C. This corresponded to a spacevelocity of approximately 343. The effluent from the tube was condensedand titrated for acid. The efliuent was found to contain 5 percentS-hexenoic acid.

Example 11 Epsilon-caprolactone. was fed through the tube described inExample I at a rate of 280 nil/hr. at a temperature of 550 C; (spacevelocity equals 560). The tube effluent which condensed was titratedwith base and was found to'contain 19 percent S-hexenoic acid.

Example III Titration'with base indicated. a purity of96 percent:.cal'-culated. as 6.-heptenoic. acid. An examination. of: theinirared spectrumof this product indicatedthat the double was" in the terminal'position.Very little ("estimated 5 percent) absorption characteristic of transinternal doublebonds' was observed.

Example I V The tube used in Examples I, II and III was coated on theinside with lsolute cement and after drying was packed with 5 mm. glassbeads. Through this tube was passed 500 gramsofepsilon-caprolactone at arate of 160 ml./hr. at an average temperature of 560 C. The spacevelocity was approximately 335. There wasobtained 475 grams. of tubecondensate. Analysis indicated thatv the reaction mixture contained 17.4percent. of 5.-hexenoic acid.

Example V A sample of epsilon-caprolactone (200 grams) was passedthrough the tube used in Example IV at a temperature of 625 C. and arate of mL/hr. (space velocity equals 223).. The tube effluent (127grams) containing 32.6. percent 5-hexenoic acid as indicated byanalysis.

Example VI A sample of epsilon-caprolactone (300 grams) was fed throughthe tube usedin Examples IV and V at a rateof 50 mL/hr; at a temperatureof 575 C. (space velocity equals. 104). The tube efiiuenti (235 grams)contained 2617- percent S-hexenoic acid as indicated by analysis; Thetube products from Examples IV, V and VI were composited and distilledunder reduced. pressure. There was isolated S-hexenoic acid, boiiing at-84 C. at 4mm. and having a refractive index of 1.4331.

Example VII A sample of 'epsilon-methyl-epsilon-caprolactone (585grams)" was fed through the tube used in Examples IV, V and VI at ml./hr. at a temperature of 535 C; (space velocity equals 277) The tubeefiiuent (553 grams)- contained- 82.2 percent 6-heptenoic acid asindicated by analysis. Distillation of the reaction mixture gave thesame product as obtained in Example Hi.

What is claimed is:

1. A process for the production of olefinically-unsaturated organic.acids which comprisespassing an epsiloncapro'lactone corresponding tothe general formula:

wherein, R, R R andY represent hydrogen atoms and lower alkyl. groupscontaining from 1 through 8 carbon atoms, except that when R and R areboth hydrogen; Y is hydrogen, at; a space velocity in the range of fromabout 20 liters/liter/hour to about 3000 liters/liter/hour through aheated reaction zone maintained at a temperature inthe range of fromabout 400 C. to about 600 C.

3. A process for the production of delta-hexenoic acid to thesubstantial exclusion of gamma-hexenoic acid which comprises passingepsilon-caprolactone at a space velocity in the range of from about 20liters/liter/hour to about 3000 liters/liter/hour through a heatedreaction zone maintained at a temperature in the range of from about 400C. to about 600 C.

4. A process for the production of epsilon-unsaturated acids to thesubstantial exclusion of delta-unsaturated acids which comprises passingan epsilon-lower-alkylepsilon-caprolactone at a space velocity in therange of from about 20 liters/liter/hour to about 3000 liters/liter/hour through a heated reaction zone maintained at a temperature in therange of from about 400 C. to about 600 C.

5. A process for the production of epsilon-unsaturated acids to thesubstantial exclusion of delta-unsaturated acids which comprises passingepsilon-methyl-epsiloncaprolactone at a space velocity in the range offrom about 20 liters/liter/hour to about 3000 liters/liter/hour througha heated reaction zone maintained at a temperature in the range of fromabout 400 C. to about 600 C.

6. A process for the production of olefinically-unsaturated acids whichcomprises pyrolyzing an epsilon-methylepsilon-caprolactone.

7. A process for the production of an olefinically unsaturated organicacid which comprises pyrolizing an alkyl-epsilon-caprolactone.

8. A process for the production of olefinically-unsaturated organicacids which comprises heating an epsiloncaprolactone corresponding tothe general formula:

RaYRRR ll'n'n'tl 0 wherein, R, R R and Y represent hydrogen atoms andlower alkyl groups containing from 1 through 8 carbon atoms, except thatwhen R and R are both hydrogen, Y is hydrogen, at a temperature in therange of at or above the boiling point of said lactone to about 800 C.

9. A process for the production of olefinically-unsaturated organicacids which comprises pyrolyzing an epsilon-caprolactone correspondingto the general formula:

iii Milli wherein, R, R R and Y represent hydrogen atoms and lower alkylgroups containing from 1 through 8 carbon atoms, except that when R andR are both hydrogen, Y is hydrogen, to a temperature sufficiently highto crack the epsilon-caprolactone and produce anolefinically-unsaturated organic acid.

12. A process for the production of an olefinicallyunsaturated organicacid which comprises heating an epsilon-caprolactone corresponding tothe general formula:

wherein, R, R, R, and Y represent hydrogen atoms and lower alkyl groupscontaining from 1 through 8 carbon atoms, except that when R and R areboth hydrogen, Y is hydrogen, to a temperature sufficiently high tocrack the epsilon-caprolactone to produce the olefinically-unsaturatedacid.

References Cited in the tile of this patent Van Natta et al.: I. A. C.8., vol. 56 (1934), page 455-7.

Brown et 9.1.: J. A. C. 8., vol. 66 (1944), page 839.

1. A PROCESS FOR THE PRODUCTION OF OLEFINICALLY-UNSATURATED ORGANICACIDS WHICH COMPRISES PASSING AN EPSILONCAPROLACTONE CORRESPONDING TOTHE GENERAL FORMULA: